LLDP agent

When you enable LLDP on the switch, it is automatically enabled on all data plane interfaces. You can customize this setting behavior by manually enabling/disabling support on each interface.

Supported standards

The LLDP agent supports the following standard: IEEE 802.1AB-2005, Station, and Media Access Control Connectivity Discovery

Operating modes

An LLDP agent can operate in one of the following modes:

  • TxRx mode: An LLDP agent in this mode can send and receive LLDP frames.
  • Tx mode: An LLDP agent in this mode can only send LLDP frames.
  • Rx mode: An LLDP agent in this mode can only receive LLDP frames.
  • Disable mode: An LLDP agent in this mode cannot send or receive LLDP frames.

An LLDP agent operating in TxRx mode or Tx mode sends LLDP frames to its directly connected devices both periodically and when the local configuration changes.

Sending LLDP frames

Each time the LLDP operating mode of an LLDP agent changes, its LLDP protocol state machine reinitializes. A configurable reinitialization delay prevents frequent initializations caused by frequent changes to the operating mode. If you configure the reinitialization delay, an LLDP agent must wait the specified amount of time to initialize LLDP after the LLDP operating mode changes.

Receiving LLDP frames

An LLDP agent operating in TxRx mode or Rx mode confirms the validity of TLVs carried in every received LLDP frame. If the TLVs are valid, the LLDP agent saves the information and starts an aging timer. The initial value of the aging timer is equal to the TTL value in the Time To Live TLV carried in the LLDP frame. When the LLDP agent receives a new LLDP frame, the aging timer restarts. When the aging timer decreases to zero, all saved information ages out.

TLV support

By default, the agent sends and receives the following mandatory TLVs on each interface:

  • Port ID
  • Chassis ID
  • TTL

By default, the agent sends and receives the following organizationally specific TLV (IEEE 802.1) on each interface:

  • Port description
  • System name
  • System description

  • Management address

  • System capabilities
  • Port VLAN ID